1. Field of the Invention
The present invention relates to apparatus for establishing a relatively uniform charge level on charge-retaining material, in general, and to such apparatus for establishing a uniform charge level on a moving web of such material, in particular.
2. Description of the Prior Art
The presence of electrostatic charges on charge-retaining materials causes problems in many industries. In the photographic industry, for example, electrostatic charges on potential photographs or film units within a light-tight film cassette containing a plurality of film units for use in an "instant" type photographic camera, such as that sold by Polaroid Corporation, Cambridge, Mass., under its registered trademark SX-70, will often cling to one another with such intensity as a result of tee force of attraction developed by such electrostatic charges, that proper ejection of an exposed film unit from said film cassette can be prevented if the effects of such charges are not controlled. In the SX-70 photographic film units mentioned above, for example, electrostatic charges are controlled by controlling the charge levels on components of said film prior to final film unit assembly.
In my copending U.S. patent application, Ser. No. 183,326, filed Sept. 2, 1980, a brush-like device is employed to establish a desired electrostatic charge level on a moving web of charge-retaining material by passing said web through a relatively intense electrostatic field generated by said device when it is electrically connected to a relatively low potential DC source of suitable magnitude and polarity. A similar but more limited disclosure of said brush-like device is contained at page 70 in the February, 1980, issue of "Research Disclosure".
A limitation of electrostatic charge-controlling conductive bristle brush apparatus presently employed to establish an electrostatic charge on charge-retaining material is the inability to place an electrical potential on such a brush that is much in excess of 4.5 KV without generating a corona on said conductive bristle brush. While corona might be acceptable in many charge-retaining material, charge-controlling applications, it is generally unsuitable for use with materials that are sensitive to light such as materials incorporated in many photographic products. In addition, corona produces ozone, and ozone has an odor that may be offensive to personnel in the vicinity of the corona source.